Because of their mechanical properties titanium alloys are widely, if not exclusively, used in the fabrication of compressor hardware for gas turbine engines. Such hardware includes blades and vanes which cooperate to compress air which is subsequently combusted with the addition of hydrocarbon fuel to provide motive power. Gas turbine engine compressors generally comprise a multiplicity of sets of blades and vanes which cooperate to progressively compress air. The number of stages may range from about 5 to about 20. In a modern gas turbine engine the compressed air may reach temperature of up to 1400.degree. F., pressures of up to 450 psi and velocities of up to 1000 ft. per minute. Thus, it can be appreciated that compressor hardware, especially towards the end of the compression process operates in a demanding environment.
Efficient compressor operation demands the maintenance of the original compressor hardware geometry. The compressor blades and vanes have airfoil shapes with relatively sharp edges. Gas turbine engines ingest vast quantities of air and this air will inevitably include some amount of particulate material. In the case of aircraft this may be sand or grit from the runway. Such materials are very abrasive and erosive when they impact compressor hardware at high speeds. The erosion process is detrimental as it reduces the compressor efficiency because of the degradation of the starting airfoil geometry.
This problem has been appreciated for some time and attempts have been made to employ hard coatings on compressor hardware surfaces to reduce erosion. Such coatings are generally more or less effective in controlling erosion but they have all heretofore had a significant detrimental effect on the high cycle fatigue behavior.
Compressor blades and vanes operate in a high energy moving gas stream and are subject to a variety of vibrational effects. Due to these conditions and the inherent properties of titanium, many compressor components have lives which are fatigue limited. Thus any detriment in fatigue life resulting from a hard coating cannot be tolerated.
Therefore, a need exists for an erosion resistant coating which does not reduce the fatigue properties of gas turbine components.